(a) Technical Field
The present invention relates to a method of variably controlling a transmission pattern of a hybrid vehicle. More particularly, the present invention relates to a method of controlling a transmission pattern of a hybrid vehicle, which converts a transmission pattern into a pattern that sufficiently secures engine charge power by considering the total amount of electric load when the transmission pattern is determined in accordance with a current state of charge (SOC) state.
(b) Background Art
The hybrid vehicles among eco-friendly vehicles promote the reduction of exhaust gas and the improvement of fuel efficiency by selecting a motor as well as an engine as a power source. Hybrid vehicles require a high efficiency and performance power transmission system which transmits the engine power or the motor power separately or simultaneously to the drive wheels.
FIG. 4 is a view illustrating an exemplary power transmission apparatus for a hybrid vehicle according to the related art. As shown in FIG. 4, a typical power transmission device for a hybrid vehicle includes an engine 10 and a motor 12 connected in series, an engine clutch 14 arranged between the engine 10 and the motor 12 to transmit or interrupt the engine power, a controller (not shown) configured to connect and disconnect of the clutch based on the driving situation, an inverter 20 configured to convert a battery current into an alternating current (AC) voltage and apply the AC voltage to the motor 12, an automatic transmission 16 configured to transmit the power of the motor or motor and engine to a drive wheel, and a Hybrid Starter Generator (HSG) 18 connected to a crank pulley of the engine to start the engine and generate electricity.
The automatic transmission is a stepped-speed transmission, the transmission pattern of which is determined by various factors. The factors determining the type of transmission pattern in a hybrid vehicle equipped with the stepped-speed transmission include inclination, temperature condition, State of Charge (SOC), driver selection mode, battery discharge limit condition, and drive mode determination. However, under the condition that the power consumption of the electric field load, air conditioner, and Electric Oil Pump (EOP) of a vehicle increases, a battery charge loss may occur, and the fuel efficiency may be reduced due to inefficient control and operation for charging a battery.
FIG. 1 is a flowchart illustrating a process of determining a transmission pattern in a hybrid vehicle according to the related art. As shown in FIG. 1, when the engine cooling water is less than a specific temperature, or the external temperature is less than a specific temperature, the transmission pattern is determined as a transmission pattern for prompt warm-up under a low temperature of winter season. Additionally, when determined as a battery discharge limit situation, the transmission pattern is determined as a transmission pattern for complementing a motor assist output deficiency due to the battery discharge limit
Furthermore, to determine the transmission pattern, it is determined whether the battery charge state meets the SOC reference condition. When the battery charge state meets the SOC reference condition, a predetermined transmission pattern is determined based on drive modes (e.g., extremely congested, congested, normal, national highway, expressway, etc.) based on the driver intention. On the other hand, when determined as not meeting the SOC reference condition, a low SOC transmission pattern is determined to promote the battery charge.
Referring to FIG. 2, the process of determining the transmission pattern by determining whether the SOC reference condition is met includes inputting drive mode into a transmission pattern determining part 100 using a lookup table 102, and inputting a current battery SOC into the transmission pattern determining part 100, and determining, by the transmission pattern determining part 100, the transmission pattern based on the current SOC and the drive mode.
In particular, when the current SOC is equal to or greater than a particular boundary value, the transmission pattern determining part 100 switches on similar to a relay and outputs “1”, thereby determining the transmission pattern matching with the drive mode based on driver intention. When the current SOC is equal to or less than a particular boundary value, the transmission pattern determining part 100 switches off similar to a relay and outputs “0”, thereby determining a low SOC transmission pattern that can promote the battery charge.
However, in the foregoing process of determining the type of the transmission pattern, since the electric load (e.g., electric field load+air conditioner load+EOP load) of a vehicle is not considered, when the identical engine power is output upon increase of electric load of a vehicle under the identical condition, the SOC of a battery becomes insufficient, leading to reduction of the fuel efficiency.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.